The present invention relates to ultrasonic welding of electrical wires to terminals. More particularly, the present invention relates to ultrasonic welding of wires to terminals through the insulation jacket of the wires.
Ultrasonic welders are known in the art, as exemplified by U.S. Pat. No. 5,772,100, 4,867,370 and 3,053,124. This class of devices utilizes ultrasonic energy to join metals, particularly nonferrous metals used in the electrical arts, as for example the splicing of wires and the attachment of a wire to a terminal. Ultrasonic welding is not actually xe2x80x9cweldingxe2x80x9d in the sense that there is no application of heat as is used in conventional welding, wherein metals are heated to the point of melting into each other. In the case of ultrasonic welding, a mechanical vibration is applied to the metals, typically in the preferred frequencies of 20 kHz or 40 kHz.
The frequency and the amplitude of the vibration cause the metals to mutually gall at their contact surfaces. This galling results in contaminants, such as for example surface oxidation, to be displaced. The galling further causes the contact surfaces to be polished. As galling continues, the contact surfaces become intimate, whereupon atomic and molecular bonding occurs therebetween, thereby bonding the metals together with a weld-like efficacy (ergo, the term xe2x80x9cultrasonic weldingxe2x80x9d).
A number of considerations determine the efficacy of the metal-to-metal surface bond, the major considerations being the amplitude of the vibration, the applied force and the time of application. These variables collectively define the efficacy of bonding between the contacting metal surfaces. The applied power (P) is defined by the amplitude (X) of vibration times the force (F) applied normal to the metal surfaces (P=FX), and the applied energy (E) is defined by the applied power (P) times the time (t) of application (E=Pt). These variables are predetermined to achieve the most efficacious bond based upon the metals and the particular application.
To provide reliable and predictable bonds by ultrasonic welding, ultrasonic welders include power supplies and actuators controlled by a microprocessor. An example thereof is the xe2x80x9cULTRAWELD(copyright)/40xe2x80x9d ultrasonic welder of AMTECH(copyright) (American Technology, Inc.) of Milford, Conn. This class of commercially available ultrasonic welders include: a power supply, a transducer where electrical energy is converted into mechanical vibration, an amplitude booster where the mechanical vibrations are amplified, and an output tool in the form of a horn which tunes the vibrations to a tip. The tip is aligned with a stationary anvil, and the ultrasonic welder includes one or more actuators which allow for movement of the tip relative to the anvil. Preferably, the tip and the anvil are knurled so as to grip the metals placed therebetween.
In operation of a conventional ultrasonic welder, a wire is stripped of its insulation jacket at an end section, and the stripped end section is then placed adjacent a top surface of a base of a terminal to which it is to be bonded. The operator places the stripped section of wire and terminal into the ultrasonic welder, such that the a bottom surface of the base rests upon the anvil and the stripped section of the wire is aligned with the tip. The operator then causes the sonic welder to automatically sequence.
A typical sequence for bonding a wire to a terminal may go as follows: the tip descends onto the stripped section of wire and applies a compressive force between it and the anvil (compressing the stripped section of wire onto the base of the terminal), the location of the tip relative to the anvil is sensed, and if within tolerances, the transducer is actuated so as to apply ultrasonic vibration to the tip for a preset time. Finally, the tip is retracted away from the stripped section of wire. The result is a bond of the stripped section of wire relative to the top surface of the base of the terminal in an area defined generally by the tip area.
A typical sequence for splicing a first wire to a second wire may go as follows: the wires are stripped and then compressed along a horizontal axis, the tip descends onto the stripped section of the wires and applies a compressive force between it and the anvil (compressing the stripped section of the wires along a vertical axis), the location of the tip relative to the anvil is sensed, and if within tolerances, the transducer is actuated so as to apply ultrasonic vibration to the tip for a preset time. Finally, the tip is retracted away from the stripped section of the wires. The result is a bond of the stripped section of the wires relative to each other in an area defined generally by the tip area.
While ultrasonic welding methodologies have advanced considerably in recent years, there remains a universal perception that before ultrasonic welding can occur, the insulation jacket must first be stripped off from the wire. One believed reason for this perception is that while ultrasonic welding is capable of removing surface contaminants, a wire insulation jacket is obviously quite different from mere surface contamination in comparative terms of both the quantity and quality of the material, such that it cannot be regarded simply as a xe2x80x9ccontaminantxe2x80x9d which is capable of being dissipated during application of ultrasonic vibration.
The present invention is a methodology for applying ultrasonic welding processes to insulation jacketed wires without firstly stripping them. A preferred acronym therefor is xe2x80x9cUWTIxe2x80x9d (Ultrasonic Welding Through Insulation).
The ultrasonic welding methodology according to the present invention is counter-intuitive, in that it has been discovered that a conventional ultrasonic welding apparatus is capable of providing an ultrasonic bond between a wire and another metal surface through the insulation jacket of the wire.
During the process according to the present invention, the insulation jacket is melted. Accordingly, the insulation jacket must be of a meltable material, as for example a thermoplastic, preferably for example a PVC or a polyester.
According to a method of the present invention, an insulation jacketed wire (multi-stand or single stand) with its insulation jacket thereon and intact is placed upon a top surface of a base of a terminal to which it is to be bonded and the staking wings of the terminal are stacked down onto the insulation jacketed wire. The operator places the insulation jacketed wire and terminal into a conventional ultrasonic welder, such that the a bottom surface of the base rests upon the anvil and the insulation jacketed wire is aligned with the tip. The operator then causes the sonic welder to automatically sequence.
A typical sequence for bonding the insulation jacketed wire to the terminal may go as follows: the tip descends onto the section of wire and applies a compressive force between it and the anvil (compressing both the wire and the insulation jacket onto the base of the terminal), the location of the tip relative to the anvil is sensed, and if within tolerances, the transducer is actuated so as to apply ultrasonic vibration to the tip for a preset time, and finally the tip is retracted away. During application of the ultrasonic vibration, the insulation jacket melts and is entirely displaced and dissipated between the wire and the base of the terminal as the tip presses forceably toward the anvil. The result is a bond of the wire relative to the top surface of the base of the terminal in an area defined generally by the tip area.
Accordingly, it is an object of the present invention to provide an ultrasonic weld of a wire to a secondary metal through the insulation jacket of the wire.
This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment.